There are several commonly known methods for terminal sterilization, including, dry heat, steam autoclave, ethylene oxide (EO) and radiation (gamma and E-beam). There are also newer sterilization options that utilize hydrogen peroxide (H2O2) vapor which are effective sterilization methods for highly resistant spore formers, non-spore forming bacteria and other microorganisms.
However, many of these traditional sterilization methods suffer from a number of limitations which reduce their effectiveness. For instance, the application of dry heat is typically conducted at 160-170° C. for a minimum of two hours but due to its high temperature requirement, its application is highly limited for temperature-sensitive devices and instruments.
Another sterilization method utilizes steam autoclave which is the oldest and typically most cost-effective method of sterilization used mostly for surgical instruments. The applied steam reaches 121-148° C. in a pressure chamber at 15 PSI. The sterilization period is dependent on the temperature and size of the load and can range from 10-60 minutes. Yet because this method utilizes relatively high temperatures, it is not well suited for heat sensitive materials, devices, and instruments.
Another methods utilizes Ethylene Oxide (ETO) gas for items that are heat or moisture sensitive. Although the operating temperature of this process is far below those of dry heat and steam autoclave sterilization, it may still be too high for a certain medical devices, namely bioabsorbable stents.
Gamma and E-beam sterilization is another method which uses radiation where the effect on polymeric materials is the same for both. Gamma and E-beam sterilization typically subjects devices to irradiation sterilization but polymeric devices, in particular, will inevitably be affected by the radiation and will experience changes in their polymer structure (such as chain scission and cross-linking). These processes may lead to significant changes and compromise in the tensile strength, elongation at break, and yield strain of such polymeric devices. Furthermore, the exact changes in mechanical properties may not be immediately apparent as there can be some time delay in the development of these changes.
Another sterilization further includes Vaporized Hydrogen Peroxide (VHP) sterilization which has been generally applied for sterilizing medical devices in hospitals worldwide. Sterilization by VHP occurs in a relatively low-moisture environment at a temperature less than 50 C. It is generally suitable for sterilizing heat and moisture-sensitive items and delicate instruments. Hydrogen Peroxide is an oxidizing agent that effects sterilization thru oxidation of key cellular components (e.g. membrane lipids, DNA, and other essential constituents). These chemical interactions at multiple biologically important reaction sites are believed to be responsible for the inactivation of microorganisms. As a low-temperature gaseous method of sterilization, VHP is an alternative to ETO sterilization but VHP sterilization does not penetrate into the devices to be sterilized as much as ETO. However, besides low-temperature and moisture, VHP sterilization does offer other significant advantages over ETO sterilization including excellent material compatibility and short cycle time. Yet like other sterilization modalities, VHP has limitations. Because VHP sterilization lacks the penetration available with ETO, an open gas pathway must be present. Medical devices such as PTCA or PTA catheters with or without stents mounted on to the delivery catheters may comprise relatively long tubular members in a range of 100-150 cm with luminal diameters as small as 0.008″. Such configurations present a significant challenge for this method of sterilization as VHP sterilization is generally incapable of penetrating and sterilizing though these lumen lengths.
Because of these limitations, there is a need for a method that is capable of sterilizing devices with complex geometry and high-sensitivity to temperature and radiation exposure.